Method and apparatus for dividing pulverous material into desired fractions by means of a rotating sifting machine



March 20, 1951 KARL-AXEL cs. GUSTAVSSON 2,546,068

METHOD AND APPARATUS FOR DIVIDING PULVEROUS MATERIAL INTO DESIRED FRACTIONS BY MEANS OF A ROTATING SIFTING MACHINE Filed July 15, 1948 Patented Mar. 20, 1951 METHOD AND APPARATUS FOR DIVIDING PULVEROUS MATERIAL INTO DESIRED FRACTIONS BY MEANS OF A ROTATING SIFTING MACHINE KarL-Axel Goran Gustavsson, Enkoping, Sweden Application July 15,1948, Serial No. 38,806 In Sweden February 23, 1948 Claims. (Cl. 209-145) The present invention relates to a method and an apparatus for dividing pulverous material into desired fractions and the invention is an improvement and development of the method in which the division into fractions is carried out in a wind sifting machine having a rotating sifting chamber and in which the material while exposed to centrifugal action is subject to the action of a rotating gas current controllable as to capacity and velocity and flowing towards the centre in a direction opposite to the centrifugal force.

In this method it has been proved that the air flowing spirally into the sifting chamber of the wind sifting machine is subject to a retardation close to the walls of the sifting chamber causing, especially in apparatus of small dimensions, a certain impurity in the produced fractions.

According to the invention this disadvantage is eliminated by causing the sifting chamber of the wind siftin machine to rotate with a number of revolutions so adapted that the gas current flowing spirally inwards at a certain radial distance from the centre of rotation of the sifting chamber obtains the same tangential velocity as the Walls of the sifting chamber at this point and by introducing the pulverous material into the sifting chamber at or near this point. Thus, the tangential velocity of the walls and the gas flow are synchronized at this point in the determining zone of the sifting chamber in which the particles according to their centrifugal velocity are either carried in towards the centre or out towards the periphery.

Other characteristics of the invention will be further described in the following with reference to the embodiment illustrated in the accompanying drawing in which I designates an electric motor carried by the frame 2. The entire sifting machine is mounted on the motor shaft 3 so that every part of the machine is rotated at the same speed. The sifting machine consists of ahousing 6 provided with two collecting chambers 4 and 5. At the bottom of the housing 6 there is an air inlet 8 provided with an adjustable choking member '1. The housing carries a disk 9 .by means of a'number of annular plates [0, arranged one above the other and adapted to cause a uniform fiow of the air passing to the sifting chamber. Close above the disk 9 a second disk H is arranged so as to form between the two disks an unbroken slit l3, having a central inlet I2 and a circumferential discharge opening l8 for the material. A third disk l4 projects radially from the housing 6 over the disk ll forming the sifting chamber 20 between said disk M on one side and the disks Sand H on the other side. A fan is formed on the opposite side of said disk I4 by means of a number of blades I1 and a disk I6 integral with the disk H through the hub l5. The sifting chamber communicates with the space in which the fan is disposed through an annular passage 23.

The radial distance from the centre of the discharge opening i8 is so arranged in proportion to other dimensions of the apparatus and with respect to the speed of the motor, that the tangential velocity of the air current in the sifting chamber drawn spirally towards the centre by means of the fan It, I6, I! substantially corresponds to the tangential velocity of the disk 9, I l at the discharge opening [8.

The disturbances in the air current caused by the friction against the walls of the sifting chamber at the point where the material is introduced are eliminated by this device. As previously stated this is of special importance as the particles should not be subject to any more or less uncontrollable forces at this point.

The material which is fed through the stationary funnel I9 is drawn through the central charge openin 12 and by centrifugal force symmetrically thrown out through the unbroken slit l3 to the discharge opening l8. A certain amount of transportation air may also be drawn through the charge openin l2. The air flow rectifier I0 which naturally may be constructed in many other ways, for instance with vertical slots or as a perforated disk, a wire netting or the like, causes a symmetrical and uniform flow of air, besides allowing the air to reach the desired tangential velocity under a relatively low velocity in radial direction before it is introduced in the sifting chamber 20.

The coarse fraction of the pulverous material, which is thrown out of the sifting chamber during sifting is collected in the chamber 4, in which it is pressed fast against the outer wall by centrifugal force and from which wall it may be knocked down into the trough 2|. The finer fraction which is conveyed through the fan is discharged by centrifugal force into the chamber 5 having such dimensions that the radial and axial components of the air velocity are small enough to allow the pulverous material to lodge on the outer Walls of the chamber. After being knocked down into the trough 22 the material may be removed and exposed to weighing and microscopic examination. By also weighing the such a small axial extent that the mixture of pulverulent and air by friction against the walls of the slit is brought into a'r'otation, which when 1 the mixture is introduced into thesifting cham-' ber substantially corresponds'to the rotation of the air in the sifting chamber.

Having now particularly-describedthe nature of my invention and the manner of its operation, what I claim is:

1. In an air separator for grading finely divided material in lights and heavies;-the-co'mbination of a pair of plate members mounted for rotation about acom'mon axis and disposed parallel to eachother and spaced apart to form an annular'substanti'ally slit-shaped separation chamber betweenthe plate members, drive means for rotating said plate members, conduit means for admitting air into said chamber along the circumference thereof, guide means rotatable about said rotational axis and included'in said conduit means,said guide means including a plurality of guide elements arranged to divide the airflow in a plurality of substantially parallel aircurrents for imparting air flowing through said conduit means, an approximately'uniform rotational velocity about 'said rotational axis approximately equal to the rotational velocity of said plate members about the said axis, suction means communicating with said chamber through a port in one of the plate members near the rotational axis of the latter for producing a spiral flow of air through the chamber toward the rotational axis thereof, the other of said plate members including a circular slit having an inlet port, feed means communicatingwith said inlet port for delivering material to be graded into said circular slit, the said plate member further including'an annular outlet port communicating with the slit therein'andthe separating chamber for delivering material from the slit into the said chamber; said annular slit outlet being disposed at a'radial distance from the rotational axis at which distance'the tangential velocity of the air flowing in spirals through the separating chamber corresponds approximately to the rotational velocity'of the plate member portions defining thesaid slit outlet, and a'settling chamber encompassing the circumference of the separating chamber for collecting heavies ejected from the separating chamber by centrifugal force, the lights being discharged from the separating chamber through said port thereof near the rotational axis.

2. An air separator as described in claim 1, wherein the said guide elements comprise a plurality of annular discs mounted for conj-oint rtati'on about said rotational axis and disposed parallel to each other spaced apart.

3. An air'separator as described inclaim '1, wherein said suction means comprise'a'centrifugal fan having fan blades mounted for rotation aboutsaid rotational axis and disposed behind the separating chamber as seen in the'dire'c'tion of the airflow.

4. An air separator as described in' claim 1, in combination with a third plate member mounted adjacent to and spaced apart from the plate member having said port near the rotational axis to form an annual chamber between the said plate member and the third plate member, and fan blades mounted for rotation about said rotationa-l'axis and=disposed withinsaid last mentioned annular chamber, said 'fan blades being set for drawing air through the said plate port.

5. An air separator as described in claim 1, in 'combination with a second settling chamber disposed on the discharge side of said suction means forbolle'c'tin the light passing through the suction means;

6. An airseparator as described in claim 1, in combination with a third plate member mcuntedadjacen't to and spaced apart from the plate member having said port near the rotational-axis to form an annular chamber between the said plate member and the third plate member, fan blades mountedfor rotation-about said rotational --aXis and disposed within said last mentioned annular-chamber, said fan blades beingset for drawing air through the saidinlet port, and asecond settling chamber encompassing the said annular fan chamber for collecting'the'lights ofthe-materialto be graded.

7. An-air separator -as--described in claim 1, in combination with a-choke member adjustably a mounted within-said conduit means for regulating the airflow rate through'said -conduit means.

8. An air separator forgrading'finelydivided materialinlights and-heavies; comprisin a'shell mounted rotatably about an axis, drive means for rotating-shell, :saidshell including an annular comparatively narrow separating chamber extending radially from the'shell 'axi's andmounted for rotation in-unison with the shell concentrically with the shell axis; saidchamber being open'along it's' -circumference'and having "an air outlet radially spaced from the circumference of the'ch'amber, said shell further including-anair inlet for'adinittingoperational-air into the shell and" conduit-means for admitting air into said chamber along the-circumference thereof, pump means for circulating an air current"'-through said 'shell in the direction frcm the air inlet 'to the air-outlet, guide'means disposed Within said conduit means-and mounted "for rotation in unison with the 'shell and the conduit means, said guide means comprising a plurality of guideelements arranged todividetheairfiow in a plurality of substantially parallel air currentsfor imparting -'to the airflow-through said conduit means a substantially uniform rotational velocity about the shell axisapproximately equal to the rotational-velocityof the shell; conduit means for admitting materiaI 'to' be graded into the sepa rating chamber,- saidconduit *means -com'municating with 'the chainbe'r'through an inlet port for the mater'ialpositioned intermediate the chamber circumference and the air outlet of the chamber and at 'a radial distance from 'the shell axis "at whichdistance the tangential velocity of air flowing spirally-through the separating chamber toward the air outlet thereof corresponds approximately tothe rotational velocity of the said inlet port 'for the material; and a. settling chamber en'compassing' the'circumference of the separatingchamberlfor collectin heavies ejected from the separating chamber by centrifugal force,,the lights being discharged from the separating chamber'through said'outlet'p'ort thereof.

9. An air 'sepaiator asdescribed in claim 1,

wherein said inlet port for the delivery of material is positioned substantially in alignment with said rotational axis.

10. An air separator as described in claim wherein said drive means comprise an electric motor having a drive shaft protruding therefrom, said shell being operatively coupled with said shaft with the shell axis in vertical position for rotation of the shell and the components disposed therein by the motor.

KARL-AICEL GfjRAN GUSTAVSSON.

REFERENCES CITED The following references are of record in the file of this patent:

Number 15 Number Germany Jan. 2, 1922 

